1. Field of the Invention
The present invention relates to a high-density magnetic recording medium and, more particularly, to a magnetic recording medium, from which signals are reproduced, for use in a system using a magnetoresistive effect magnetic head (MR head) or a giant magnetoresistive effect magnetic head (GMR head).
2. Description of the Related Art
In recent years, what is called a metallic thin film magnetic recording medium, in which a magnetic layer is formed by coating a nonmagnetic support directly with various kinds of magnetic materials, such as magnetic metallic materials, Co—Ni alloys, Co—Cr alloys, and, metal oxide Co—CoO, through vacuum thin film forming techniques is utilized as a magnetic recording medium in the field of video tape recorders in order to achieve higher picture quality and higher recording density.
To improve the electromagnetic conversion characteristics of the magnetic recording medium so as to obtain a larger output, what is called an oblique evaporation method has been proposed, according to which the formation of a magnetic layer of the magnetic recording medium is performed by obliquely evaporating the magnetic layer. The magnetic recording medium, whose magnetic layer is formed by this method, is practically used as evaporated tape for use in high-band 8 mm video tape recorders and digital video tape recorders.
The metallic thin film magnetic recording media excel in coercive force and in squareness ratio. Because the magnetic layers thereof can be formed in such a way as to be extremely thin, the metallic thin film magnetic recording media excel in electromagnetic conversion characteristics in a short-wavelength region. Demagnetization during recording and thickness loss during reproduction are extremely small. In the metallic thin film magnetic recording media, binders, which are nonmagnetic materials, are not mixed into the magnetic layers thereof. It differs from what is called a coated magnetic recording medium in which a magnetic layer is formed by applying a magnetic coating, which is obtained by dispersing magnetic powder in the binder, on a nonmagnetic support. Thus the packing density of ferromagnetic metallic materials is increased, so that the metallic thin film magnetic recording media have an advantage in achieving high recording density.
Oblique-evaporated magnetic tape is manufactured by performing, for example, a method of making an elongated nonmagnetic support run in the longitudinal direction thereof and depositing a magnetic material on a major surface of the nonmagnetic support while the tape runs, thereby forming a magnetic layer. Thus, high productivity and excellent magnetic property can be assured.
On the other hand, as demands for magnetic recording media, such as magnetic tape, serving as data streamers rise, the magnetic recording medium has been requested to have higher recording density. Instead of a conventional inductive head used for reproducing recorded information, a magnetoresistive effect magnetic head (MR head) is applied as a magnetic head used when recorded information is reproduced. This MR head can detect micro leakage magnetic flux with high sensitivity. Thus, the MR head is effective in increasing this recording density.
Meanwhile, the MR head has a detection limit at which the sensitivity thereof against a leakage magnetic flux saturates. The MR head cannot detect a leakage magnetic flux when the leakage magnetic flux is more than a design limit of the MR head. It is, therefore, necessary to optimize the MR head by reducing the film thickness of the magnetic layer of the magnetic recording medium.
To achieve a denser magnetic recording medium, it is important to reduce medium noises by decreasing the size of magnetic fine particles constituting the magnetic layer of the magnetic recording medium and to attain the improvement of orientation of the magnetic fine particles so as to achieve high outputs thereof.
When a magnetic layer is formed in the case of magnetic tape in which a magnetic tape is formed by the oblique evaporation, the magnetic layer is formed by causing the elongated nonmagnetic support to run in the longitudinal direction thereof and depositing magnetic fine particles on a major surface of the nonmagnetic support. At that time, an angle, at which the magnetic particle incidents upon the nonmagnetic support, is optimized. The reduction in the size of the magnetic fine particles is performed by introducing a reactive gas, such as oxygen or nitrogen, into a magnetic layer forming atmosphere. Consequently, the diameter of the magnetic fine particles constituting the magnetic layer ranges from 5 nm to 20 nm or so.